Cyclopentanol (C5H10O) ,also called cyclopentyl alcohol is a cyclic alcohol. It is a colorless viscous liquid with a pleasant odor. Slightly less dense than water. 

Crystal Structure

Cyclopentanol is the simplest member of the class of cyclopentanols bearing a single hydroxy substituent.  It is a relatively simple example of a molecular material that forms plastic crystalline phases on initial cooling. 

The X-ray powder diffraction studies indicate that cyclopentanol forms two plastic crystalline phases below its melting point of 255 K. The first of these plastic phases, phase-I [a = 5.883 (1), c = 9.479 (2) A ? , Z = 2 at 243.2 K], crystallizes in hexagonal symmetry with the molecules adopting a close-packed arrangement in which each molecule rotates about its centre of mass which imposes spherical symmetry. On cooling below 236 K, the second orientationally disordered phase of cyclopentanol is formed, phase-II [a = 10.0996 (14), c = 9.500 (2) A ? and Z = 6 at 217.2 K]. In the crystal structure of phase-II, the molecules retain the same positions as they adopt in the lattice of phaseI, but complete rotational freedom is lost so that the rotation of the molecules is restricted about some fixed axis. On further cooling, rotational freedom of the molecules is lost completely and two fully ordered phases are formed. 

Uses

Cyclopentanol is used as a solvent, and as an intermediate in making perfumes, pharmaceuticals, dyes and other organic chemicals.

Reference

[1] S A MOGGACH. High-pressure polymorphism of cyclopentanol (C5H10O): the structure of cyclopentanol phase-V at 1.5 GPa.[J]. Journal of Synchrotron Radiation, 2005, 12 Pt 5: 590-597. DOI:10.1107/S0909049505021461.